1. Field of the Invention
This invention relates to amorphous metal alloys, and, more particularly, to high strength, low density titanium-beryllium base compositions.
2. Description of the Prior Art
Investigations have demonstrated that it is possible to obtain solid amorphous metals from certain alloy compositions. An amorphous substance generally characterizes a non-crystalline or glassy substance, that is, a substance substantially lacking any long range order. In distinguishing an amorphous substance from a crystalline substance, X-ray diffraction measurements are generally suitably employed. Additionally, transmission electron micrography and electron diffraction can be used to distinguish between the amorphous and the crystalline state.
An amorphous metal produces an X-ray diffraction profile in which intensity varies slowly with diffraction angle. Such a profile is qualitatively similar to the diffraction profile of a liquid or ordinary window glass. On the other hand, a crystalline metal produces a diffraction profile in which intensity varies rapidly with diffraction angle.
These amorphous metals exist in a metastable state. Upon heating to a sufficiently high temperature, they crystallize with evolution of a heat of crystallization, and the X-ray diffraction profile changes from one having glassy or amorphous characteristics to one having crystalline characteristics.
It is possible to produce a metal which is totally amorphous or which comprises a two-phase mixture of the amorphous and crystalline state. The term "amorphous metal", as employed herein, refers to a metal which is at least 50% amorphous, and preferably at least 90% amorphous, but which may have a small fraction of the material present as included crystallites.
Proper processing will produce a metal alloy in the amorphous state. One typical procedure is to cause molten alloy to be spread thinly in contact with a solid metal substrate such as copper or aluminum so that the molten metal loses its heat to the substrate. When the alloy is spread to a thickness at about 0.002 inch, cooling rates of the order of 10.sup.6 .degree. C/sec are achieved. See, for example, R. C. Ruhl, Vol. 1, Materials Science and Engineering, pp. 313-319 (1967), which discusses the dependence of cooling rates upon the conditions of processing the molten metal. Any process which provides a suitable high cooling rate, as in the order of 10.sup.5 .degree. to 10.sup.6 .degree. C/sec, can be used. Illustrative examples of procedures which can be used to make the amorphous metals are the rotating double roll procedure described in H. S. Chen and C. E. Miller in Vol. 41, Review of Scientific Instruments, pp. 1237-1238 (1970) and the rotating cylinder technique described by R. Pond, Jr. and R. Maddin in Vol. 245, Transactions of the Metallurgical Society, AIME, pp. 2475-2476 (1969).
More recently, in a patent issued to H. S. Chen and D. E. Polk (U.S. Pat. No. 3,856,513, issued Dec. 24, 1974), amorphous metal alloys at least 50% amorphous have been disclosed having the formula M.sub.a Y.sub.b Z.sub.c, where M is at least one metal selected from the group consisting of iron, nickel, chromium, cobalt and vanadium, Y is at least one element selected from the group consisting of phosphorus, carbon, and boron, Z is at least one element selected from the group consisting of aluminum, silicon, tin, antimony, germanium, indium and beryllium, a ranges from about 60 to 90 atom percent, b ranges from about 10 to 30 atom percent, and c ranges from about 0.1 to 15 atom percent. These alloys have been found suitable for a wide variety of applications including ribbon, sheet, wire, etc. The amorphous alloys also may have the formula T.sub.i X.sub.j, where T is at least one transition metal, X is at least one element selected from the group consisting of aluminum, antimony, beryllium, boron, germanium, carbon, indium, phosphorus, silicon and tin, i ranges from about 70 to 87 atom percent and j is the balance. These alloys have been found suitable for wire applications.
While these alloys are finding a wide variety of applications, there remains a need for a high strength, low density material suitable for structural applications.